Lycopene has been recently recognized as an industrially important natural food coloring agent, because of its high staining power in the red region, and because of its safety and potentially beneficial effect. Lycopene occurs naturally and abunds in a number of fruits, primarily in tomatoes and watermelon, from which it can be extracted by different extraction processes. Lycopene can also be synthesized by a variety of synthetic routes, both chemically and biosynthetically. While reference will be made hereinafter to tomatoes as the source of lycopene, for the sake of brevity, it is understood that the same applies, mutatis mutandis, to watermelon or to any other lycopene source, including synthetic lycopene.
The art recognizes the use of vegetable extracts as colorants and additives to the food industry. Spice and herbs oleoresins, for instance, are commonly employed in the food industry. For instance, U.S. Pat. No. 4,285,981 refers to the use of oleoresins as food colorants or flavoring. U.S. Pat. No. 5,019,405 teaches the use of natural colorants for the dyeing of fruit.
A number of processes have been proposed and are currently used for the extraction of oleoresins, such as paprika oleoresin, e.g., by using hexane as the extraction solvent. According to a process described in copending Israeli Patent Application No. 107999, filed Dec. 23, 1993 by the same applicants herein, the pulp obtained after the separation of waste materials and of tomato serum is fed to an extraction stage, where it is extracted to provide tomato oleoresin. Such oleoresin contains about 2-10% of lycopene, depending on the original concentration of lycopene in the tomato. Tomato oleoresin containing about 40%-100% lycopene is obtained in the form of a free-flowing powder.
The use of lycopene presents some technological and practical problems. First of all, pure crystalline lycopene is unstable on storage at room temperature, due to oxidation, and lycopene may undergo degradation with time, unless appropriate measures are taken, e.g. antioxidants are added. While food-compatible antioxidants are known and used in industry, e.g., BHT, BHA or propyl gallate, they are not a desirable addition, and they are dispensed with whenever possible. In addition, lycopene-containing formulations should be protected against microbial spoilage. Lycopene which naturally occurs in oleoresins apparently enjoys the protection of the oil and of natural antioxidants (tocopherols), originating from the tomato, but when it is dispersed in an environment. such as water, which can support microbial growth, the formulation will spoil unless it is protected by suitable means, such as by heat sterilization or the addition of preservatives. Illustrative examples of such preservatives are benzoic acid and sorbic acid.
Although lycopene exists in different forms, having different colors and intensities, the term "lycopene" is used in all cases to indicate the chemical entity. It should be noted however, that crystalline lycopene has an intense red color, and differs from dissolved or dispersed or solubilized lycopene, which has a yellow-orange color. Furthermore, lycopene naturally occurring in fruit is found in chromoplasts in crystalline form, and therefore is capable of retaining its red color, as in the tomato. Therefore, throughout this specification it is important to note to what form of lycopene reference is being made at the various stages of the process described herein.
As stated, the intense red color of lycopene is due to its crystalline form, and is influenced by its particle size distribution. Lycopene loses its staining power in the red range when the crystals dissolve, which occurs readily in a variety of organic solvents, e.g., oils, including oil found in the tomato seeds and extracted during the processing of the tomato in the course of lycopene oleoresin production. When lycopene oleoresin is solubilized in aqueous solutions, it assumes a yellowish to orange color, depending on concentration, and cannot be used to impart red color to food products.
Additionally, lycopene crystals recovered from oleoresin extraction, as described above, vary greatly in size, and contains relatively large crystals, of the order of tens of microns. Given that optimal staining power in the red color range is obtained in the 1 .mu.m to 3 .mu.m particle diameter range, in terms of light refracted from the crystals much staining power is lost if the oleoresin is used as such, as is customarily done in the art. Furthermore, one cannot effectively use the oleoresin as such, to obtain red color, since part of the lycopene is dissolved in the tomato lipids and the resulting hue will be orange.
It is therefore clear that it would be highly desirable to provide a lycopene concentrate that overcomes the aforesaid drawbacks while maintaining a high staining power.